Due to the increasing environmental restrictions on logging and diminishing supplies of high quality old growth timber, the cost of lumber has risen dramatically. In particular, clear lumber, lumber that is free of knots or other defects, has become especially valuable. Because of the increasing cost of natural clear lumber, it is desirable to provide a substitute product formed from lower cost raw material such as low grade lumber, i.e. lumber with knots, cracks, or other defects.
One way to create a long piece of clear lumber is to join small clear pieces together, usually with a joint called a finger joint. This is accomplished by cutting the short clear blocks from longer pieces of low grade lumber and joining those blocks together. The use of finger joints in the assembly of the composite board results in a product that has nearly the same strength as a naturally occurring clear board. This allows lumber that is otherwise only suitable for low value uses to be converted to high value clear lumber.
Small pieces or blocks are normally joined together with the aid of a finger jointing machine. The finger jointing machine mills or cuts fingers into each end of the blocks, applies glue to one or both ends and presses the blocks together so that the fingers on each block interlock, thus forming the final product. Most typically, the blocks are carried through the finger jointing machine on a conveyor that has a number of spaced apart lugs. The boards are placed in a spaced apart side-by-side arrangement, one in front of each lug, and the lugs carry or push the boards through the machine. For maximum efficiency it is important that each lug carry a block through the machine. Any missed lugs result in a reduced output level.
In order to have the highest recovery of clear product from low grade source lumber, it is important that the finger jointing machine be capable of working with blocks of varying length. Currently, finger jointing machines can mill and press together blocks as small as 4" in length. The same machines must also accommodate blocks 36" or longer. In order to avoid the additional step of sorting the short clear blocks into groups of uniform length, the machines are designed to accommodate blocks of assorted lengths in random order, within the above range. Thus a 4" block may directly follow a 30" block, which may in turn be followed by a 16" block. Generally a single sequence of blocks will have the same thickness and width, but a finger jointing machine can usually be set to accept various thicknesses or widths of blocks by some adjustment or modification.
In the past, partially because of the need to accommodate blocks of varying length, a human operator has been required to place each block in front of a lug, attempting to utilize every lug. In addition to being labor intensive and monotonous for the operator, this procedure is far from foolproof and many lugs go unused, thereby reducing efficiency.
After the finger joints are milled in the ends of the blocks, the blocks are placed in an end-to-end relationship on a press conveyor that carries the blocks into a pressing stage. The transfer operation from the lug conveyor to the press conveyor is known as a corner operation since the conveyors typically are oriented transversely to one another. In the past, the corner operation, like the feed operation, required a human operator to pick up each block off the lug conveyor and place it on the transverse conveyor. Thus, transferring the blocks from the lug conveyor to the transverse conveyor has been one of the more labor intensive parts of the process of creating finger jointed boards.
This invention addresses these problems by automating both the loading of the blocks in front of the lugs and the corner operation.